The role of membrane lipids in modulating B cell responses will be evaluated to understand membrane related events occurring during activation by lipipolysaccharide (LPS) and other ligands. The membrane composition of normal B cells and B lymphoma cells (BCL1) will be altered by treatment of cells with cholesterol-free lipid vesicles and vesicles containing various cholesterol:phospholipid (C/P) ratios. The effect of such treatment on the LPS mitogenic response in preliminary experiments has suggested that B cells are refractory to such treatment except in the presence of some normal spleen cell. We will determine the role of endogenous and exogenous cholesterol in the apparent inability of B cell activity to be modulated by vesicle treatment. If the resistance of B cells is reversible by control of cholesterol synthesis and utilization, the content of phospholipids and the C/P ratios of treated and untreated B cell plasma membranes will be measured to confirm that vesicle-cell interaction changes the membrane composition and to determine whether this occurs by lipid exchange or cell fusion. The viscosity of plasma membranes from treated and untreated cells will be measured by fluorescence polarization, the relevance of each physical change to biological function evaluated. If B cells are not the target for vesicle suppression, the normal cell which enables B cells to be susceptible to vesicle inhibition of LPS induced mitogenesis will be identified. If BCL1 cells are different from normal cells, the susceptibility of their mitogenic response to pharmacological inhibitors of early triggering events will be examined to determine if such early events have already occurred in this line. We will determine the time relative to mitogen interaction with cells at which vesicles are inhibitory and if this inhibition is reversible by addition of cGMP. The effect of vesicle treatment on B cells activated by other stimuli will be examined. These will include the polyclonal response to LPS, other polyclonal B cell activators, and antigen stimulated antibody responses. This combination of biochemical and immunological approaches should add to our understanding of membrane control of both various stages of B cell activation and activation signals delivered by different stimuli which may suggest mechanisms underlying aberrant cell behavior of neoplastic cells or immunocompetent cells in metabolic diseases.